As many of us enter the hottest months of the summer, this month's issue of Shock beckons with its characteristic mix of clinical and translational studies on injury, shock, resuscitation, and sepsis. Readers are invited to enjoy a cool drink while perusing a new review article, five clinical science papers, and 10 basic science articles.
As much as we like to believe that what we do in practice at the bedside has a profound and positive impact on patients’ outcomes, there comes a time to challenge the status quo. Potter et al. (1) do just that in their systematic review on the impact of vasoactive medications on microcirculatory blood flow. The authors remind us that the pathophysiology of sepsis is deranged microvascular flow, yet what we see and treat is frequently the macrovascular hemodynamic parameters of cardiac index (CI), mean arterial pressure (MAP), and end organ function such as urine output. The group from the UK pools together the available literature on the effects of vasodilators, inotropes, vasopressors, and immunomodulatory drugs on the microvasculature as measured by orthogonal polarization spectral, sidestream dark field (SDF), and incident dark field imaging. They lament the low quality of published data by GRADE methodology and note the significant risk for heterogeneity and bias in the pooled studies. These limitations lead them to conclude that despite improvements in macrocirculatory parameters by multiple drugs, the only (weak) available evidence suggests vasopressors might provide benefit for patients with chronic hypertension when the infusion is used to restore MAP to baseline. The authors implore us to consider the reasons why current data is lacking—failure to have consensus on outcomes measures and definitions, lack of study of drugs at various ranges and dosing regimens, and the timing of first administration of trial drugs. The authors are to be applauded for suggesting where we should focus our attention—on the study of pharmacotherapies to augment the microcirculation (levosimendan and nitroglycerin), and also for providing recommendations to improve study methodology.
The first clinical science article by Kawamoto et al. (2) invites us to join them in exploring how plasma extracellular vesicle (EV) expression of integrins and programmed cell death-1 (PD-1) ligands may differ in patients with systemic inflammatory response syndrome (SIRS) and sepsis compared with healthy controls. Further, the authors aim to bring bench-to-bedside with the correlation of their findings to the clinical outcomes of organ failure in their patient cohort. The detailed work by this group from Japan concludes that EV ß2 integrin expression is significantly increased in the sepsis group with corresponding reductions in blood pressure and renal function, common clinical findings in septic patients. They postulate that given ß2 integrin is expressed only on leukocytes, increased EV expression of ß2 integrin suggests enhanced leukocyte activation is a systemic process, consistent with the global inflammation seen in sepsis leading to its myriad effects. In addition, the researchers go on to describe their finding that soluble PD-L1 levels are significantly increased in the sepsis group and correlate with worsening sequential organ failure assessment scores, depressed Glasgow Coma Scores, and impaired renal function, further implicating this ligand's role with organ failure and the worsening of systemic inflammation. Though the sample sizes are somewhat small (27 patients each in SIRS and sepsis groups, 18 patients in the control) the authors are to be congratulated on a novel study that provides a sound basis for further work and challenges the reader to consider how future therapies targeted at this molecular level may have the promise to improve clinical outcomes.
Zeeshan et al. (3) bring us another thoughtful paper from the group in Tuscon regarding reversal of the coagulopathy of trauma (COT). This well-designed study used propensity score matching to retrospectively compare two cohorts of patients, one which received three-factor prothrombin complex concentrate (3-PCC) and the other which received 4-PCC to rapidly reverse COT as defined as a INR >1.5. The authors find that 4-PCC is superior to 3-PCC for rapid correction of INR, its use shaving over an hour off of reversal time. And while time is off the essence in trauma, so is cost and ultimate outcome. The group went on to study the differences in transfusion rates and overall costs as well as thrombotic complications between the groups, revealing an increased up-front cost to administer 4-PCC. This was recovered because patients required fewer later blood product transfusions, without difference in mortality or complications. Though the authors do evaluate infectious complications in their study, one can only wonder if additional complications, infectious and otherwise, are avoided by sparing patients on average three units of packed red blood cells and two units of fresh frozen plasma by utilizing 4-PCC over 3-PCC, the transfusion savings noted in the study. Another excellent study from this group, providing clinical data to support the theoretical advantages of this therapy.
Keeping with the theme of trauma, the elegant study from Coiffard et al. (4) aims to elucidate differences in the delicate circadian rhythm patterns of trauma patients with sepsis from those who do not develop sepsis. Based on their own prior work and an extensive literature review, they focus their attention on the measurement of cortisol, cytokines, leukocytes, and clock genes. Their meticulous methods demanded blood sampling precisely every 4 h for a 24 h period after admission with subsequent cytometry and spectrophotometry for analysis. Their results are displayed in clear tables and graphs to allow the reader to understand the magnitude and the rhythm of changes in septic versus non-septic trauma patients. They identify that septic patients have higher levels of cortisol and delayed time to acrophase (the cycle's peak). Differences in lymphocyte, monocyte, and neutrophil counts, TNF and two different clock genes, also significantly varied between the groups. This leads the authors to conclude that early circadian rhythm disruption is associated with sepsis in severe trauma patients and we would be wise to consider intensive care unit (ICU) interventions to preserve the body's natural rhythms, including making adjustments in the timing of daily drug administration, particularly steroids.
The vexing question of how to determine fluid status in the critically ill patient is studied by Yao et al. (5). Using the readily available and noninvasive diagnostic tool of ultrasound, the group prospectively measured the inferior vena cava (IVC) in multiple planes from multiple angles and determined both cross-sectional area and diameter indices to describe variations of the IVC throughout the respiratory cycle in 67 mechanically ventilated patients. Recognizing the nuances of anatomic IVC variability, the authors rightly stress the importance of multiple measurements of the IVC for determination of fluid status. Ultimately, they describe that IVC diameter ratio has a 89.3% positive predictive value for fluid responsiveness, while IVC area distensibility index carries a 92.3% negative predictive value, with area under the receiver operating characteristic a solid 0.829 and 0.749, respectively. The authors point out that one benefit of ultrasound measurements is the ability to evaluate patients who have arrhythmias, which are common in critically ill patients and limit the usefulness of other commercially available monitoring devices. The indices calculated in this study are simple and can be easily completed at the bedside. While this method won’t be the definitive solution to fluid status determination, this study represents yet another elegant and simple use of ultrasound, another tool in our critical care toolbox.
The next article by Rozemeijer et al. (6) is a fitting end to the clinical science section of this month's Shock, as the authors seem to draw on what we learned in the first review article: study of the microcirculation and meticulous attention to design. The group from the Netherlands seeks to understand the relationship between shock and the renal resistive index (RRI) as well as the determinants of RRI. The study includes 92 patients who had measurements of both macrocirculation, such as CVP and CI, as well as microcirculation with SDF. Ultimately, they determine a significant correlation for parameters of pressure (CVP) but not of flow (CI, sublingual microcirculation). Interestingly, they also find that the correlation to RRI with vasopressors appears to be dose dependent and that too much of a good thing can be bad, that unnecessary increases in doses of vasopressors actually lead to increases in RRI leading to acute kidney injury (AKI). Finally, they present the call for the clinician to use the readily available and noninvasive beside ultrasound to measure RRI, providing what could turn out to be an early marker of impending AKI and used to appropriately dose vasopressors.
Turning to basic science investigations, we are presented with several studies of sepsis, lung injury, resuscitation, and shock. Muscle effects—both cardiac and skeletal muscle—in sepsis models are a subtheme this month. Luptak et al. (7) from Boston explore sex differences in cardiomyopathy of sepsis, extending prior studies in endotoxemia. Mortality was similar in 15 to 35-week-old wild-type male and female FVB mice and cardiomyocyte-specific catalase over-expressing transgenic CAT mice after cecal ligation and puncture (CLP). However, hearts from CLP-injured wild-type male mice showed depressed left ventricular peak systolic pressures in ex vivo Langendorff preparations. Hearts from male CAT mice were partially protected, implicating redox-dependent and independent mechanisms in this sex-specific process. Reactive oxygen species (ROS) were attributed to induction of NOX-1, NOX-2, and COX-2. The mechanisms by which female hearts were relatively protected were not determined, however, and female hearts displayed similar increases in NOX-1 and COX-2 along with additional increases in other ROS-generating systems. Regardless, the authors suggested potential clinical implications of their observations, including potential male-specific utility of anti-oxidant therapy or estrogen therapy.
Mella et al. (8) investigated sepsis-associated neurogenic inflammation, the stimulation of an inflammatory response mediated by sensory neurons and neuropeptides. Also using a CLP mouse model, the group from Boston University demonstrate dramatic protection of neurokinin 1 receptor (NK-1R, gene name TACR1) deletion in 80-week old BALB/c female mice. Aged mice were used to mimic the higher mortality rates observed in elderly patients; indeed, the >80% mortality observed here is greatly increased versus the typical 5% mortality in young BALB/C mice. NK-1R mediates inflammation after sepsis—plasma interleukin-6 (IL-6), MIP-2, and IL-1 receptor alpha were all reduced at 24 h in NK-1R knockouts after CLP. NK-1R knockouts also displayed improved hemodynamic function and increased circulating neutrophils versus wild-type mice. These results in knockout mice are consistent with this group's prior studies showing protection of a NK-1R antagonist in wild-type mice, implicating the neurokin-1 receptor in the inflammatory and cardiovascular pathology of sepsis.
Veering a bit from the sepsis and lung injury thread running through this issue, Dogan et al. (9) study resuscitative endovascular balloon occlusion of the aorta (REBOA), a method to halt bleeding and achieve cardiopulmonary resuscitation (CPR). Using 27 anesthetized pigs, the authors test REBOA positioning in the thoracic descending aorta at the level of the heart or the diaphragm versus no REBOA, monitoring a primary endpoint of systemic arterial pressures during CPR. Based upon improved blood pressure, arterial pH, and lactate, the authors conclude that occlusion at the level of the diaphragm might be more effective, suggesting that careful determination of REBOA level is necessary for optimal outcomes.
Matters of positioning are also addressed by studies from Barcelona by López-Aguilar et al. (10). Here, the investigators test body position in 17 anesthetized pigs to determine associations with ventilator-associate pneumonia (VAP). While it is well known that patients lying fully supine in horizontal position are at higher risk of VAP, the current practice of semirecumbant positioning has been challenged and the Trendelenburg position (TP) has been advanced as superior. This latter position places the body supine on an incline with a head-down-tilt and feet elevated 15° to 30°. The authors employ a secondary analysis of a prior study to examine the effects of 30° anti-TP versus 5° TP on development of VAP and markers of brain injury. While TP decreased VAP, the authors found that TP also increased cerebral petechial hemorrhages and neuronal injury in the dentate gyrus. Thus, position matters and the authors urge further study to determine the neurological risks of long-term TP.
Aoyagi et al. (11) focus on lung injury, which is also often a consequence of sepsis. This month they report on the protective effects of etoposide and corticosteroids in their own model of acute respiratory distress syndrome (ARDS) in mice. ARDS, caused by a variety of pulmonary and systemic diseases from sepsis to pneumonia and trauma, is characterized by a rapidly progressing alveolar damage with neutrophil influx and exudate. The authors induce fatal ARDS by sensitizing mice with an activator of natural killer T cells, a-galactoslyceramide, followed by intratracheal LPS, resulting in lung hyperinflammation and infiltration of hemophagocytic cells into the bone marrow. The authors hypothesized that targeting activated macrophages rather than cytokines might improve outcomes in ARDS. Here, they use the cytotoxic agent, etoposide, and prednisolone, an anti-inflammatory corticosteroid, both alone and in combination. Results show that combination therapy improved survival, and reduced lung injury and pulmonary leukocyte influx while single-agent therapy was ineffective. Cytokines were mainly unchanged by treatments. The authors conclude that targeting inflammatory cells in ARDS holds greater promise than targeting cytokine production.
Two papers investigate the use of activated saline preparations in sepsis and injury. Zhang et al. (12) tested the effects of using an ionized gas—cold atmospheric plasma—to activate saline for use against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and in a CLP model in vivo. Plasma generated from a custom device was used to activate normal saline, decreasing pH from 6.08 to 2.17 in 5 min. Reactive species measured in the discharge plasma-activated saline (DPAS) included long-lived species such as nitrate, nitrite, hydrogen peroxide, and ozone, as well as the short-lived species nitric oxide. DPAS effectively decolonized and inactivated MRSA more potently than hydrogen peroxide, and increased survival of 4 to 5 week-old male C57BL/6 mice subjected to CLP via a 21-gauge needle and no reported analgesia or antibiotics. Bacterial load, circulating cytokines, and histopathological changes and apoptosis in lung and intestine were all reduced by DPAS treatment. The authors acknowledge that the mechanism of protection is still somewhat mysterious and that the pharmacokinetics and pharmacodynamics are unknown, a barrier to clinical development, but they assert convincingly that the dramatic effects merit further investigation.
Patients with septic shock and tachycardia experience worse survival, while significant reductions in heart rate early in resuscitation associate with improved survival. Thus Uemura et al. (13) used a canine model of endotoxic shock to investigate the safety of beta-adrenergic receptor blockade in the initial phase of hemodynamic resuscitation. Here, the investigators use low-dose landiolol to reduce heart rate while avoiding cardiovascular collapse. In this exploratory study, 13 hybrid dogs were subjected to intravenous lipopolysaccharide to induce shock and effects of landiolol on systemic hemodynamics and vasopressor and fluid requirements were investigated in a computer controlled closed-loop infusion system developed by the authors. The authors find that low-dose landiolol resulted in reduced heart rate, cardiac contractility, and oxygen consumption without changing vasopressor or fluid needs. Given these promising results, they recommend future larger studies with more relevant animal models.
Skeletal muscle pathology induced by sepsis is the focus of studies by Chen et al. (14) from Chongqiung, China. Muscle wasting and muscle dysfunction are thought to be partly responsible for the dismal outcomes sepsis survivors face after leaving the ICU, including poor quality of life, failure to return to work, and high 1-year mortality. The authors had previously noted the abnormal expression and function of fetal γ-nicotinic acetylcholine receptors (γ-nAChR) and neuronal α7-nAChR equivalent to functional denervation in a rat model of sepsis. Here, the authors interrogate the role of autophagy in this process using CLP in 2 to 3-month-old male Sprague-Dawley rats with 40% mortality. First the authors measure neuromuscular function over 24 h after CLP, documenting a steep decline in compound muscle action potentials and nerve conduction velocities over time. Expression of γ-nAChR and α7-nAChR rose alongside blood and muscle cytokines and evidence of autophagy in muscle. Treatment with rapamycin 1-h after CLP improved survival, reduced IL-6 levels and blood bacterial load, while improving muscle function and reducing γ-nAChR and α7-nAChR expression. Neuromuscular function at 7 days was also somewhat improved by this single dose of rapamycin. The authors infer a protective effect of enhancing autophagy with rapamycin, given that the autophagy inhibitor 3-methyadenine had opposite effects. Given that this is a systemic drug study, however, the precise cell and tissue targets and mechanisms resulting in rapamycin-mediated protection are difficult to discern. Nevertheless, both the characterization of the immediate and longer term muscle dysfunction and the protective effects of rapamycin are significant contributions to the literature.
Like the Luptak study, Li et al. (15) investigate cardiac consequences in sepsis, although here the focus is the alpha-1 adrenergic receptor and its agonist phenylephrine. Using an in vitro system of cardiomyocyte cultures treated with LPS, the authors demonstrate reduced markers of apoptosis in cells pretreated with phenylephrine. Rats treated with subcutaneous phenylephrine 3 h after CLP also demonstrated improved survival and reduced markers of cardiomyocyte apoptosis concomitant with increased pro-survival protein Bcl2, reduced apoptotic protein Bax, and increased phosphorylation of ERK1/2. Although this was a systemic drug administration model that cannot rule out interactions mediated by other cell types or tissues or signaling through other receptors, the authors conclude that phenylephrine signaling on cardiomyocytes activates ERK1/2 and inhibits the NF-kB, p38-MAPK, and JNK pathways, reducing dysfunction and promoting survival in sepsis.
Finally, Zou et al. (16) unite two themes by studying lung injury prevention using a different form of activated saline. They examine the therapeutic potential of hydrogen-infused saline in a treatment model of lung injury induced by limb ischemia and reperfusion. Hydrogen gas has shown protective effects in cerebral ischemia models. Here, hydrogen-rich saline (HRS) is used to deliver high levels of hydrogen to tissues without the dangers associated with hydrogen gas. Using a lethal injury approach where 75% of rats died over 4 days after 3 h of bilateral femoral artery ligation and 2 h of perfusion, the authors tested effects of HRS on pulmonary edema, tissue inflammation, and cytokines. Using 20 rats per group, HRS improved survival and reduced lung histopathology. These salutary effects were associated with reduced levels of the proinflammatory protein chimerin and NLRP3 in the lung. The authors suggest the results have implications for understanding and preventing lung injury with crush injury-induced ischemia or in limb ischemia during abdominal aortic aneurism surgery.
Reading all of the articles through this issue illumines the diversity in approaches to the experimental modeling of sepsis. Luptak et al. (7) used 13 to 35-week-old male and female FVB mice (quite a substantial age range) and 25 or 28-gauge needles to puncture the cecum four times, administering buprenorphine and 0.5 mL warm saline every 12 h but no antibiotics. Mella et al. (8) modeled sepsis in the treated elderly patient by using 80-week-old BABL/c female mice, two punctures with a 25-gauge needle and expression of stool, with administration of buprenorphine, 1 mL saline, and imipenem every 12 h. In contrast, Zhang et al. (12) tested their plasma activated saline using 4 to 5-week-old male C57BL/6 mice with no reported analgesia or antibiotics. Both studies of rats used 2 to 3-month-old male Sprague-Dawley rats. Li et al. (15) induced injury with five punctures by an 18-gauge needle and fecal extrusion, giving intraoperative saline and buprenorphine but no antibiotics, while Chen et al. (14) used a 24-gauge needle and fecal extrusion, administering a single injection of saline for resuscitation but no analgesia or antibiotics. Although different approaches might be justified by different experimental questions, the considerable variance from study to study highlights the difficulty and potential pitfalls of interpreting results across models. The reader is referred to the reviews and proposed standardized guidelines in preclinical sepsis models published earlier this year in Shock(17–21).
1. Potter EK, Hodgson L, Creagh-Brown B, Forni LG. Manipulating the microcirculation in sepsis – the impact of vasoactive medications on microcirculatory blood flow: a systematic review. Shock
2. Kawamoto E, Masui-Ito A, Eguchi A, Soe ZY, Prajuabjinda O, Darkwah S, Park EJ, Imai H, Shimaoka M. Integrin and PD-1 ligand expression on circulating extracellular vesicles in systemic inflammatory response syndrome and sepsis. Shock
3. Zeeshan M, Hamidi M, Kulvatunyou N, Jehan F, O’Keeffe T, Khan M, Rashdan L, Tang A, Zakaria E-R, Joseph B. 3-factor versus 4-factor PCC in coagulopathy of trauma: four is better than three. Shock
4. Coiffard B, Diallo AB, Culver A, Mezouar S, Hammad E, Vigne C, Nicolino-Brunet C, Dignat-George F, Baumstarck K, Boucekine M, et al. Circadian rhythm disruption and sepsis in severe trauma patients. Shock
5. Yao B, Liu J-y, Sun Y-b, Zhao Y-x, Li L-d. The value of the inferior vena cava area distensibility index and its diameter ratio for predicting fluid responsiveness in mechanically ventilated patients. Shock
6. Rozemeijer S, Haitsma Mulier JLG, Röttgering JG, Elbers PWG, Spoelstra-de Man AME, Tuinman PR, de Waard MC, Oudemans-van Straaten HM. Renal resistive index: response to shock and its determinants in critically ill patients. Shock
7. Luptak I, Croteau D, Valentine C, Qin F, Siwik DA, Remick DG, Colucci WS, Hobai IA. Myocardial redox hormesis protects the heart of female mice in sepsis. Shock
8. Mella JR, Stucchi AF, Duffy ER, Remick DG. Neurokinin-1 receptor deficiency improves survival in murine polymicrobial sepsis through multiple mechanisms in aged mice. Shock
9. Dogan EM, Beskow L, Calais F, Hörer TM, Axelsson B, Nilsson KF. Resuscitative endovascular balloon occlusion of the aorta in experimental cardiopulmonary resuscitation: aortic occlusion level matters. Shock
10. López-Aguilar J, Bassi GL, Quilez ME, Martí JD, Ranzani OT, Xiol EA, Rigol M, Luque N, Guillamat R, Ferrer I, et al. Hippocampal damage during mechanical ventilation in Trendelenburg position: a secondary analysis of an experimental study on the prevention of ventilator-associated pneumonia. Shock
11. Aoyagi T, Sato Y, Toyama M, Oshima K, Kawakami K, Kaku M. Etoposide and corticosteroid combination therapy improves acute respiratory distress syndrome in mice. Shock
12. Zhang J, Qu K, Zhang X, Wang B, Wang W, Bi J, Zhang S, Li Z, Kong MG, Liu D, et al. Discharge plasma-activated saline protects against abdominal sepsis by promoting bacterial clearance. Shock
13. Uemura K, Kawada T, Zheng C, Li M, Sugimachi M. Low-dose landiolol reduces heart rate and cardiac oxygen consumption without compromising initial hemodynamic resuscitation in a canine model of endotoxin shock. Shock
14. Chen J, Min S, Xie F, Yang J, Wang X. Enhancing autophagy protects against sepsis-induced neuromuscular dysfunction associated with qualitative changes to acetylcholine receptors. Shock
15. Li H, Xing Y, Yang D, Tang X, Lu D, Wang H. Alpha-1 adrenergic receptor agonist phenylephrine inhibits sepsis-induced cardiomyocyte apoptosis and cardiac dysfunction via activating ERK1/2 signal pathway. Shock
16. Zou R, Wang M-H, Chen Y, Fan X, Yang B, Du J, Wang X-B, Liu K-X, Zhou J. Hydrogen-rich saline attenuates acute lung injury induced by limb ischemia/reperfusion via down-regulating chemerin and NLRP3 in rats. Shock
17. Remick DG, Ayala A, Chaudry IH, Coopersmith CM, Deutschman C, Hellman J, Moldawer L, Osuchowski MF. Premise for standardized sepsis models. Shock
18. Zingarelli B, Coopersmith CM, Drechsler S, Efron P, Marshall JC, Moldawer L, Wiersinga WJ, Xiao X, Osuchowski MF, Thiemermann C. Part I: Minimum Quality Threshold in Preclinical Sepsis Studies (MQTiPSS) for study design and humane modeling endpoints. Shock
19. Libert C, Ayala A, Bauer M, Cavaillon J-M, Deutschman C, Frostell C, Knapp S, Kozlov AV, Wang P, Osuchowski MF, et al. Part II: Minimum Quality Threshold in Preclinical Sepsis Studies (MQTiPSS) for types of infections and organ dysfunction endpoints. Shock
20. Hellman J, Bahrami S, Boros M, Chaudry IH, Fritsch G, Gozdzik W, Inoue S, Radermacher P, Singer M, Osuchowski MF, et al. Part III: Minimum Quality Threshold in Preclinical Sepsis Studies (MQTiPSS) for fluid resuscitation and antimicrobial therapy endpoints. Shock
21. Osuchowski MF, Ayala A, Bahrami S, Bauer M, Boros M, Cavaillon JM, Chaudry IH, Coopersmith CM, Deutschman CS, Drechsler S, et al. Minimum Quality Threshold in Preclinical Sepsis Studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis. Shock